In an offshore platform installation, a grout seal is typically utilized to seal the annulus between a pile sleeve inner surface and a pile outer surface and against a high column of concrete during the grout hardening period. FIG. 1 illustrates a deepwater offshore platform with extended legs from water surface to sea floor and a plurality of skirt pile sleeves for housing piles. As shown in FIG. 1, an offshore platform deck 1 is supported by a jacket 2 extended from water surface 6 to sea floor 5. A plurality of pile sleeves 4 are attached to the bottom of the extended legs to house a plurality of piles 3, which are driven into sea floor 5 to provide the anchoring to the platform.
A grout seal is usually located at the bottom of a skirt pile sleeve 4 near sea floor. The seal has to be rugged and highly reliable because any seal failure such as grout leaking could cause the connection failure between a pile sleeve and a pile. Consequently, it could result in the foundation failure of the platform.
Existing Grout Seals for Offshore Structures
In general, there two types of grout seals for pilings in offshore jacket installation: 1) an active grout seal type such as an inflatable packer, and 2) a passive grout seal type such as a CRUX grout seal or a mechanical grout seal.
Inflatable Packer
Inflatable packer was introduced to offshore industry in 1970's and it has been widely utilized in offshore platform fields. Today, inflatable packers still occupy a very large percentage of grout seal market, especially in deepwater platform applications. Inflatable packer is an active assembly which requires a control system above water surface to activate the seal by injecting air or water to form a sealing function. FIG. 2 is an ISO cross section view of a typical inflatable packer used as a grout seal. As an active seal, the seal element is in a retracted position without making contact between the seal outer surface and a pile prior to pile lowering and inserting. As shown in FIG. 2, an inflatable packer element 8 is fixed to the inner wall of a sleeve 4 in a non-inflated condition; an injection tubing 7 is attached at the outer wall of the sleeve 4. To prevent mud at sea floor to pollute grout during pile driving, a mud wiper 9 is usually installed below the packer element 8.
In installing an offshore jacket, common practice utilizing an inflatable packer is to fabricate the jacket on land with jacket leg members and with inflatable packers installed at the bottom of skirt sleeves as grout seals. The jacket is then towed to an installation site for installation. U.S. Pat. No. 3,468,132 to Harris, issued on Sep. 23, 1969, describes a traditional inflatable packer assembly. Until today, this type of active grout seal is still widely used in offshore jacket installation applications.
An inflatable packer is composed of three subsystems in addition to the packer assembly located at the bottom of a pile sleeve: a power subsystem and a high pressure air/water injection subsystem and a piping subsystem. There are two major disadvantages for using an inflatable packer assembly as a grout seal: 1) the assembly is very expensive in terms of yard installation, yard testing and field operation; 2) the assembly is very complicated which could have potential damages in each of the three subsystems during jacket site installation. U.S. Pat. No. 4,279,546 to Harris, issued on Jul. 21, 1981, describes some of these potential damages for an inflatable packer during field operations.
Passive Seals
A typical passive seal is CRUX annular seal, as described in British Pat. No. GB2194006 to Philip et al., issued on Feb. 24, 1988. The seal assembly has an outer head portion attached at the sleeve inner wall and a bulbous ring functioning as a seal element. FIG. 4 illustrates a CRUX annular seal element 19 prior to piling activities. As shown, a guide shim 16 is attached to the inner wall of sleeve 4. An outer head portion 18 is fixed to the sleeve 4 inner wall with an inside cavity 17. A bulbous ring 20 with a fiber core forms the sealing function. The inner diameter of the bulbous ring 20 is less than the outer diameter of a pile so that the deformed ring produces compression force against the pile outer surface to form a sealing function when a pile is driven through the ring. FIG. 5 is a partial cross-section view of a CRUX annular seal when a pile 3 is driven through and a column of grout 13 is poured between the pile 3 and pile sleeve 4. As shown in FIG. 5, the bulbous ring 20 is deformed and the annular seal element 19 is bended against the pile 3 outer surface, which has several levels of shear keys 21, to form a seal for a poured column of grout 13.
A passive seal is significantly less expensive than an inflatable packer. However, the common concerns for this type of seals are the protection and the reliability of the seals during offshore pile installation activities such as pile inserting and pile driving. The pile bottom outer edge could function as a knife to damage the resilient section between the bulbous ring 20 and the outer head portion 18 due to dynamic heave motions of a pile during pile lowering and inserting.
A traditional mechanical grout seal is also a passive seal. A traditional mechanical grout seal is usually only used for shallow water applications because it could not take potential dynamic loading from shear keys which are commonly welded both on the pile top outer surface and on the sleeve inner wall of a deepwater platform for increasing the concrete bonding strength between the sleeve and the pile. A mechanical seal is composed of an annular rubber tubular wall with multiple equally spaced steel bars passing through the rubber tubular wall. These steel bars are bounded and fixed with the rubber tubular wall through a vulcanization process. The bottom of the tubular wall is fixed at the sleeve inner wall and each steel bar top passes through a steel ring which is fixed at the sleeve inner wall. As a result, each steel bar top should be able to slide up and down inside the corresponding steel ring.
FIG. 3 is an ISO cut-off section view of a typical mechanical seal with a driven pile and a column of grout poured in the annulus between a pile and pile sleeve above the seal. As shown in FIG. 3, a mechanical seal element 15, which has an annular inner diameter less than the outer diameter of the pile 3, is attached to the inner wall of the sleeve 4. A plurality of steel bars 11 are through and bonded with the resilient seal element 15 and slides upward through the rings 12 which are fixed at the sleeve 4 inner wall. The seal element 15 forms a seal for the poured column of grout 13 between the pile 3 outer surface and the inner surface of the sleeve 4 during pile 3 grouting. A plurality of tapered guide shims 16 are placed above the seal element 15. The seal element 15 also prevents the mud 14 pollution during pile 3 driving.